Air springs for aerospace

Springs in aerospace motion control are used in the control systems that move ailerons, elevators, and rudder. If there is a major system failure, two very large springs will help deploy the ram air turbine, a mechanism that gives the pilot limited power to glide the plane for an emergency landing. The engines of the aircraft also require many springs. They are used in the landing gear and brake assemblies, passenger and cargo doors. Less critical springs are also found throughout the interior and the cargo section.

Most aircraft manufacturers require their spring suppliers to be AS9100 approved. This will ensure that proper procedures are followed from initial review of the drawings, through manufacturing and inspection

Aircraft designers need strong but lightweight materials - and springs are no exception. Springs can also see large temperature fluctuations, and need to function at very cold temperatures. Corrosion resistance is important, as the springs must not rust over the aircraft lifetime.

The most common spring material is stainless 17-7. High tensile strength and good corrosion resistance, as well as a large working temperature range, makes this an ideal choice. Another common material is titanium - high strength and low elastic modulus make this attractive when space is limited. Titanium is a very lightweight material, making this cost-effective for larger springs. High-temperature materials such as Inconel may be used in the engines.

Beryllium Copper (BeCu) is a highly conductive, non-ferrous metal alloy, making it an ideal choice for contact and spring applications. With heat-treating, the strength and durability of the metal is increased, attractive for hazardous environments, military, and aerospace. Beryllium Copper is a pliable with high electrical conductivity. It is one of the easier metals to photo-chemically machine or etch, though a bit more challenging than pure copper.

Is a compression, extension, torsion, or other type of spring required? After the approximate dimensions of the spring are determined, the spring should be designed based on the rate and loads required. The operating environment of the spring also must be considered.

First the material is chosen, and then the wire size is estimated. The stresses in the material at minimum and maximum loads are then calculated and compared to the tensile strength of the material. There are spring design guidelines that require the stresses to be below a certain percent of the tensile strength. A spring is considered overstressed when the corrected stress percent exceeds the recommended percentage of the ultimate tensile strength. Critical springs may require cycle testing to verify spring fatigue life.